1. Technical Field
The present invention relates to a liquid ejecting head that ejects liquid by driving piezoelectric elements and a liquid ejecting apparatus including the liquid ejecting head. In particular, the invention relates to a liquid ejecting head and a liquid ejecting apparatus that are capable of suppressing damage of the piezoelectric elements.
2. Related Art
A liquid ejecting apparatus is an apparatus that includes a liquid ejecting head and ejects various types of liquids from the liquid ejecting head. As the liquid ejecting apparatuses, there are image recording apparatuses such as an ink jet printer and an ink jet plotter, for example. In recent years, the liquid ejecting apparatus is also applied to various types of manufacturing apparatuses by using such technology for the liquid ejecting apparatus that it can make an extremely small amount of liquid land at a predetermined position accurately. For example, the liquid ejecting apparatus is applied to a display manufacturing apparatus for manufacturing a color filter of a liquid crystal display and the like, an electrode forming apparatus for forming an electrode of an organic electro luminescence (EL) display, a field emission display (FED), and the like, and a chip manufacturing apparatus for manufacturing a biochip (biochemical element). Further, a recording head for the image recording apparatus ejects liquid-like ink and a coloring material ejecting head for the display manufacturing apparatus ejects solutions of coloring materials of red (R), green (G), and blue (B). An electrode material ejecting head for the electrode forming apparatus ejects a liquid-like electrode material and a bioorganic compound ejecting head for the chip manufacturing apparatus ejects a solution of a bioorganic compound.
The above-mentioned liquid ejecting head has a configuration in which liquid is introduced to pressure chambers, pressure fluctuation is generated on the liquid in the pressure chambers, and the liquid is ejected through nozzles communicating with the pressure chambers. The above-mentioned pressure chambers are formed on a crystalline substrate made of silicon or the like by anisotropic etching with high dimensional accuracy. Further, piezoelectric elements are used preferably as pressure generation units for generating the pressure fluctuation on the liquid in the pressure chambers. There are piezoelectric elements having various configurations. For example, each piezoelectric element is configured by forming a lower electrode at the side closer to the pressure chamber, a piezoelectric layer made of a piezoelectric material such as lead zirconium titanate (PZT) and an upper electrode in a laminated manner by a film formation technique. One of the upper and lower electrodes functions as an individual electrode provided for each pressure chamber and the other of them functions as a common electrode common to the plurality of pressure chambers. Portions of the piezoelectric layers that are sandwiched by the upper and lower electrodes correspond to active portions that are deformed by application of a voltage to the electrodes. Portions of the piezoelectric layers with which any one of the upper and lower electrodes is not overlapped or neither of the upper and lower electrodes is overlapped, correspond to passive portions that are not deformed by the application of a voltage to the electrodes.
Opening portions of the pressure chambers at one side (opposite side to the nozzle surface side) are closed by an elastic film made of SiO2 and having flexibility, for example, and the piezoelectric elements are formed on the elastic film through an insulating film (for example, ZrO2). The elastic film and the insulating film function as a vibration plate. In the existing technique, irregular and complicated deformation such as undulation of the piezoelectric elements and the vibration plate is generated on both end portions thereof in the lengthwise direction of the pressure chambers in some cases when the piezoelectric elements are driven. There has arisen a problem that liquid ejection stability is adversely influenced by the irregular and complicated deformation. Furthermore, a stress is concentrated on boundary portions between the active portions and the passive portions of the piezoelectric elements due to the irregular vibration and damage such as a crack is generated on the piezoelectric elements in some cases. In order to address this, for example, JP-A-2010-208071 (FIG. 2C) proposes a configuration in which a metal layer as a weight is provided on the upper electrode (second conductive layer) so as to suppress irregular vibration on the end portions of the piezoelectric elements. In the configuration as described in JP-A-2010-208071 (FIG. 2C), lead electrode portions (fourth conductive layers) that are electrically connected with the lower electrodes (first conductive layers) are provided in the vicinity of one end portion of the upper electrode with slight spaces between the lead electrode portions and the upper electrode and piezoelectric layers are exposed therebetween.
In the manufacturing process of the liquid ejecting head as described in JP-A-2010-208071 (FIG. 2C), when the pressure chambers are formed on the single-crystal silicon substrate by anisotropic etching processing, a pressure chamber plate before the pressure chambers are formed thereon is immersed in an etchant such as potassium hydroxide (KOH). To be more specific, the pressure chamber plate is immersed in a state where the vibration plate and the piezoelectric elements have been laminated and formed on the surface (upper surface) of the pressure chamber plate, which is opposite to the surface (lower surface) on which etching is to be performed. In the liquid ejecting head manufactured through the process, a phenomenon that the piezoelectric layers on the above-mentioned exposure portions are burned out has occurred. The piezoelectric elements are immersed in the etchant in a state of being sealed by a protection member called sealing plate and being further protected by a protection sheet through which liquid does not penetrate. However, hydrogen gas generated at the time of etching reaction penetrates through the protection sheet and the sealing plate and comes around the side of the piezoelectric elements in some cases. If the hydrogen gas reacts with the exposure portions of the piezoelectric layers to melt the piezoelectric layers, leakage of an electric current occurs between the upper electrode (or metal layer thereon) and the lead electrode portions easily. Consequently, due to this electric leakage, it is considered that the piezoelectric layers on the above-mentioned exposure portions are burned out.